1. Field of the Invention
This invention relates to a submerged entry nozzle (SEN) for steel and, in particular, to a casting nozzle having a flat taper.
More specifically, this invention relates to a flat continuous casting nozzle particularly preferred as a thin slab continuous casting submerged entry nozzle (SEN).
2. Description of Related Art
In casting steel, a submerged entry nozzle (SEN) is used in order to prevent oxidation of molten steel. A flat SEN having a lateral width extended toward the bottom so as to be suitable for continuous casting of a thin slab or plate has been used for a long time.
FIG. 5 shows a conventionally used flat continuous casting SEN, wherein a side view showing the long edge side is on the left, and a side view showing the short edge side on the right. In FIG. 5, a flat SEN 1 has a flange 3 on the upper part, and the flange 3 is engagingly locked to a locking fitting 4, whereby the SEN 1 is engaged with the tundish nozzle 2. The respective corresponding positions of the left side view and the right side view of FIG. 5 are mutually connected by broken lines, and tapered parts 5, 6 of the SEN are formed so that the respective terminal positions are mutually conformed on the long edge side and short edge side of the SEN as shown in the drawing.
As a result of various examinations for the generating form of thermal stress with respect to such a conventional SEN in which the terminal positions of the tapered surfaces of a flat SEN are mutually conformed, it was recognized that stress concentration exists in the taper terminal positions of the nozzle. This was confirmed also by finite-element analysis based on the physical properties shown in Table 1.
TABLE 1 ______________________________________ Physical Properties of Member Used for Analysis ______________________________________ Bulk Density 2.37 Thermal Expansion (%) (1000.degree. C.) 0.29 Young's Modulus (kgf/cm.sup.2) 0.09 .times. 10.sup.6 Poisson's Ratio 0.2 Thermal Conductivity (cal/cm.deg.sec) 12.1 ______________________________________
Under the boundary condition for analysis that molten steel of 1540.degree. C. is poured into a nozzle inner hole at an outside air temperature of 30.degree. C., the stress generated in the nozzle was calculated. The analysis was performed with a 1/4 divided nozzle as a model. A constraining force of 4.4 kg/cm.sup.2 was imparted to the flange on the nozzle upper end. Thus, in the stress analytic result, the stress generated in the neck part, which is based on constraining force, is excluded from the examination of the generated stress by the coincidence of the taper terminal parts.